Persistence and Effect of TMTD on Soil Respiration and Nitrification In Two Nursery Soils BY M. A. RADWAN
Abstract.
Persistence of tetramethylthiuram disulfide
(TMTD)
and its effect on
activity of soil microflora in general and on nitrifying micro-organisms in particular were investigated in soils from two tree nurseries in western Washington. TMTD was depleted in both soils; rate of depletion depended on initial concentration of the chemical and action of soil micro-organisms. Addition of some commercial fertilizers enhanced depletion. Use of these fertilizers or addition of well-decomposed organic matter in the nursery would probably increase degradation of TMTD in soil. TMTD decreased soil respiration.Soils responded differently to treatment, but initial depressions of C02 pro duction in both soils were proportional to concentration of TMTD in soil. Following initial inhibition in two treatments, respiration was stimulated, probably due to utiliza tion of decomposition products of T MTD by micro-organisms. Nitrification was im paired by TMTD for 20 days but by 60 days had recovered completely in almost all cases. Effects of TMTD reaching the soil during spray operations with a repellent formulation containing the chemical do not seem serious, and even beneficial effects seem possible under some conditions.
T ETRAMETHYLTHIURAM DISUJ,FIDE (TMTD), in various spray formulations, has been recommended for treatment of planting stock before lifting from nursery beds (Besser and Welch 1959, Duffield and Eide 1962) to protect planted seed lings from damage by wild mammals, particularly hares and rabbits. A number of forest nurseries in the Pacific North west have adopted this technique, and each year millions of seedlings are sprayed. However, the mechanical equip ment used also deposits large amounts of spray on seedbed soil (Duffield and Eide 1962). TMTD has successfully controlled several soil-borne diseases (McKeen 1950, Cram and Vaartaja 1957) and, at the rates recommended, is reported to change
soil microbiological balance (Richardson 1954) with little or no phytotoxic effects (Kendrick and Zentmyer 1957). Yet little is known of the chemical's persistence and effects as related to its use as a repellent in forest tree nurseries. Objectives of this study were, therefore, to investigate per sistence of TMTD in soil and effect of the chemical on soil respiration and nitrifi cation. The author is Plant Physiologist, Division of Timber Management Research, Pacific North west
Forest
and
Range
Expt. Sta.,
Forest
Service, U. S. Dept. Agric., Portland, Oreg. For materials provided for this study, acknowledg ment is due to E. I. du Pont de Nemours & Co., Wilmington,
Del.; State Dept.
Natural
Re
sources, Olympia, Wash.; and Industrial Forestry Association, Portland,
Oreg.
Manuscript
re
ceived July 7, 1964.
About This File: This file was created by scanning the printed publication. Misscans identified by the software have been corrected; however, some mistakes may remain. 152 I Forest Science
'FABLE 1. Some characteristics of soils studied.1 Cation Nursery sampleJ
pH
exchange
Moisture
Organic
Clay
capacity
equivalent
matter
content
Meq/100 g
-------Percent--------
Webster
6.1
14 . 1
16.0
4.3
Greeley
5.9
19.9
25 . 0
3. 5
1
7.4 22.4
Each value is an average of two determinations.
Materials and Methods
Persistence Studies
Soils were collected at L. T. Webster and Colonel W. B. Greeley forest nurseries in western Washington. In each case, com posite soil samples of the surface 6 inches were taken from areas where TMTD had not been applied. Samples were then air dried, individually mixed, screened through a 4 mm sieve, and stored at room temperature in polyethylene bags. To characterize the soils, samples were analyzed (Table 1) by the following methods: reaction (pH) electrometrically in a 1:1 soil-water suspension (Peech et al. 1947); cation exchange capacity by a modification of the ammonium acetate method of Schollenberger and Simon (1945); moisture equivalent by the cen trifuge method of Briggs and McLane (1907); total organic matter by the dichromate oxidation method (Peech et al. 1947, Jackson 1960); and clay con tent by the hydrometer method (Bouy oucos 1927).
Two experiments were carried out. In the first, TMTD at 300 and 600 parts per million by weight (ppmw) was thoroughly mixed with autoclaved (15 psi for 3 hours, 121° C) and non-autoclaved 50-g ovendry samples of the two soils in 250-ml Erlen meyer flasks. The autoclaved soils were treated with TMTD under aseptic con ditions, and moisture of all samples was raised to the moisture equivalent with sterile water. Duplicate samples of each treatment were immediately analyzed for TMTD. All remaining flasks, lightly stoppered with cotton plugs to permit aeration, were incubated in a randomized block design at 28° ± 1° C in a water jacketed incubator, and soil moisture was maintained at the moisture equivalent by periodic additions of sterile water. At the end of 20, 60, 100, 140, and 180 days, TMTD was analyzed in duplicate samples of each treatment.
Determination of TMTD in Soil
TABLE 2. Recovery of TMTD from soil.
Known amounts of TMTD were added to 50-g (ovendry basis) soil samples, and recovery was immediately determined by a modification of Keppel's method (1959). In each case, TMTD was extracted with chloroform, and aliquots of extracts were treated with cuprous iodide. Absorbance of resulting solutions was then measured in a spectrophotometer at 440 mu and amount of TMTD determined from a previously constructed calibration curve. Recovery data are summarized in Table 2.
Percent recovery TMTD level No. deter----------- (ppmw)1
ruinations
Range
Aver.
Webster nursery
300
4
91-93
92
600
4
89-95
92
Greeley nursery
300 600
1
4 4
86-92
89
88-90
89
Parts per million by weight.
volu,me11,nu,mber2,196l!
I
153
The second experiment was to deter mine the effect of two commercial fer tilizers-ammonium nitrate (33-1/2-0-0) and ammonium phosphate-sulfate (16 20-0)-on persistence of TMTD. In this case, 50-g soil samples in 250-ml Erlen meyer flasks were either treated with fertilizer at 1,000 ppmw or left without treatment. All samples were then treated with TMTD at 300 ppmw, thoroughly mixed, and maintained at moisture equivalent throughout the test. TMTD was determined immediately and at 20, 60, and 100 days following incubation at 28° ± 1° C. As in the first experiment, two replications and a randomized block design were adopted. Soil Respiration and Nitrification Experiments
Influence of TMTD on total microbial activity was measured by determination of C02 evolved from treated and un treated soil samples. In this experiment, 100-g (ovendry basis) portions of each soil were placed in 250-ml Erlenmeyer flasks. Soils were treated with TMTD at 0, 180, 480, 720, and 1,200 ppmw,1 mixed, and brought to moisture equiva lent with water. The flasks, connected to a manifold supplying moist, C02-free air, were then incubated at 28° ± 1° C. During incubation, moisture was main tained at moisture equivalent, and C02 liberated by respiration of soil micro organisms was swept out of the flasks, trapped in 125-ml Erlenmeyer flasks con taining 1N-NaOH, and determined by differential titration with IN and 0.1 N HC1 according to Cooper's method (1941). Measurements of C02 were made on the same flasks at 20- to 40-day inter vals during a 180-day incubation period. A randomized split plot design was used with two replications. Soils and TMTD 1 These rates are comparable to concentra tions of TMTD in the surface 6 inches of soil when 0, 15, 40, 60, and 100 percent of a 10-per
concentrations were main plots, and time intervals for C02 determinations were subplots. Effect of TMTD on nitrification was studied using 100-g samples (ovendry basis) of the two soils in 250-ml Erlen meyer flasks. TMTD at 0 and 180 ppmw and an ammonium N source at 0 and 100 ppmw of N were thoroughly mixed with soil. Nitrogen sources, NH40H and (NH4)2S04, were added to the soil in volumes of water necessary to raise soil moisture to the moisture equivalent. Also, with (NH4)2S04, sufficient CaCOa was added to neutralize acids produced during nitrification (Chandra and Bollen 1961). Flasks of all treatments, lightly stoppered with cotton plugs to permit aeration, were incubated in a randomized block design at 28° ± 1° C. Moisture lost during incubation was replaced periodi cally, and duplicate samples were ana lyzed for nitrate N by the phenoldisul fonic acid method (Harper 1924) 20, 40, and 60 days following treatment. Results and Discussion Persistence of TMTD in Soil
recovery. Amount of TMTD recovered immediately after addition of the chemical averaged 92 percent in the Webster soil and 89 percent in the much heavier textured Greeley soil. High clay content of Greeley soil (Table 1) appar ently made extraction of TMTD more difficult. Recovery, however, was not affected by initial concentration of TMTD (Table 2) or soil sterilization (Fig. 1). Initial
Effect of soil type. TMTD was broken down in both soils. The chemical, how ever, was depleted more rapidly in Greeley soil except during the 20- to 60-day incubation period, when Webster lost significantly2 more TMTD. Depletion of TMTD in both soils varied with initial concentration of 2
In this paper, "significant" is used in a statis
tical sense and means that a relationship was
cent TMTD spray formulation reaches the soil
shown to exist at the 5-percent level of proba
during spray operations.
bility or lower.
154
I
Forest Science
RECOVERY OF TMTD lOOPERCENT
WEBSTER SOIL 80
---- ....
20
Autoclaved Nonautocl aved QL____L___J
____
---L----L-------
--------
----
100
GREELEY SOIL
60
Autoe laved Non auto cia ved 40
20
O L---�----�-0
20
40
6Q
80
100
140
180
DAYS
PERIOD OF INCUBATION
FIGURE 1. Recovery of TMTD initially and at different time intervals after addition of the chemical at 300 and 600 ppm by weight to autodaved and non-autr,claved soils.
Recoverie.r are expres.red a.r perc ent of
TMTD originalZv added.
volume 11,number 2, 1965
1
155
RECOVERY OF TMTD 100 PERCENT I
Soils: Webster
Greeley Untreated Nitrate Phosphate· sulfate
80
60
40
20
0
20
100
60
DAYS
PERIOD OF INCUBATION FIGURE 2. Recovery of TMTD initially and at different time intervals after addition of the chemical at 300 ppm by weight to fertilizer-treated and untreated samples of the soils. Recoveries are expressed as percent of TMTD originally added.
TMTD. Throughout the incubation period, TMTD frorn the 600 pprnw treatments in Webster soil was broken down at a slower rate than that from the 300 ppmw treatments. Similar but less marked results were observed with Greeley soil during the first 120 days following treatment. This trend suggests that under conditions of this experiment TMTD inhibited depletion factors and higher initial concentrations increased inhibition.
of autoclaving soil. Autoclav ing affected persistence of TMTD, and the effect varied with time, soil, and initial TMTD concentration (Fig. 1). During early stages of incubation, rate of TMTD decomposition was signifi cantly reduced by autoclaving, especially in Webster soil, and with the 600 ppmw treatments of each soil. However, this effect tended to disappear during later stages of the study. Effect
156
1
Forest Science
Micro-organisms, or some product of microbial activity apparently were im portant in decomposing TMTD in soil. Micro-organisms capable of breaking down TMTD were probably present in each soil. Further, higher decomposition rates of the chemical in Greeley soil suggest that greater microbial activity occurred in that soil than in Webster soil (Fig. 3). Autoclaving eliminated most micro-organisms present in the soil and resulted in reduced rates of depletion of TMTD. However, higher decomposition rates of the chemical were soon reestab lished in all autoclaved samples as soils became contaminated with air-borne microbes and as the introduced micro organisms and those that had escaped autoclaving multiplied.
Effect of fertilizers. Effect of fertili zation on persistence of TMTD in soil is shown in Figure 2. The fertilizers had no
Mg C EVOLVED AS C02 PER 100 g SOIL PER DAY 1.2
1.0
WEBSTER SOIL
0.8
0.6
0.4
0.2
0 L----J-----L--�--L-
1.8
\
\ \ \
1.6
GREELEY SOIL
\\\\
1.4
1.2
0 180 480 720 1,200 ppmw TMTD
1.0
\, 0.8
__ ---._
...... '----..... ...... ', '
0.6
"''--
0.4
""'
............ ""'
..............
"- -
.................. ;;
.... ----- -----
----
0.2
0
20
40
60
80
100
140
180 DAYS
TIME AFTER TREATMENT
FIGURE 3. Effect of TMTD on carbon dioxide evolution from two .
